The present invention relates to semiconductor memory circuits and to charge pumps in particular. Moreover, this invention relates to a power supply circuit and particularly to systems including pumped power supplies.
System designs are routinely constrained by a limited number of readily available power supply voltages (V.sub.CC). For example, consider a portable computer system powered by a conventional battery having a limited power supply voltage. For proper operation, different components of the system, such as display, processor, and memory components employ diverse technologies which require power to be supplied at various operating voltages. Components often require operating voltages of a greater magnitude than the power supply voltage and, in other cases, a voltage of reverse polarity. The design of a system, therefore, includes power conversion circuitry to efficiently develop the required operating voltages. One such power conversion circuit is known as a charge pump. The demand for highly-efficient and reliable charge pump circuits has increased with the increasing number of applications utilizing battery powered systems, such as notebook computers, portable telephones, security devices, battery-backed data storage devices, remote controls, instrumentation, and patient monitors, to name a few.
Inefficiencies in conventional charge pumps lead to reduced system capability and lower system performance in both battery and non-battery operated systems. Inefficiency can adversely affect system capabilities, e.g., limited battery life, excess heat generation, and high operating costs. Samples of lower system performance include low speed operation, excessive operating delays, loss of data, limited communication range, and inability to operate over wide variations in ambient conditions including ambient light level and temperature.
In addition to constraints on the number of power supply voltages available for system design, there is an increasing demand for reducing magnitudes of the power supply voltages. The demand in diverse application areas could be met with highly efficient charge pumps that operate from a supply voltage of less than five volts.
Such applications include memory systems backed by 3 volt standby supplies, processor and other integrated circuits that require either reverse polarity substrate biasing or booted voltages outside the range of 0-3 volts for improved operation. As supply voltage is reduced, further reduction of supply of switching components paves the way for new and more sophisticated applications. Consequently, the need for high efficiency charge pumps is increased because voltages necessary for portions of integrated circuits and other system components are more likely to vary over a wide range.